Quote:
Originally Posted by ixtab
You're right... but actually, it's a bit different. I had assumed so far that only the PID (which is in turn derived from the serial number) constitutes the key, in which case it would indeed have been even worse than what I wrote above (the PID is really only 7 characters + "*" + 2-character checksum), and those 7 characters don't even span the entire possible range (O and 0 are excluded).
However, providing the correct PID, but a wrong serial number, also fails to decrypt the file. Thus, the key space is more likely to be something like 36^13 again, which leads back to the first calculation, multiplied by another factor of ~ 50000 (yes, the serials are 16 characters, but there are only few valid "prefixes")
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Ah - I see where your confusion has come from.
The various sites that claim to generate a PID from a Kindle serial number are only useful for Kindle 1 and early firmware Kindle 2.
Kindles, since the later Kindle 2 firmwares, have not had a per-device PID. Instead the Kindle's serial number is combined with information from the book's metadata to produce a per-book 8 digit PID.
A similar mechanism is used for Kindle for PC and Kindle for Mac, and I think for Kindle for Android, using some IDs from the PC or Mac instead of a Kindle serial number.
Only Kindle for iOS still (until very recently) used a fixed PID for all kindle ebooks on the device, which was derived from the iOS device's UUID.
However, since Apple have banned the use of the UUID by iOS apps, new installations of Kindle for iOS use some new method of key generation.
But all the methods eventually lead to a 8-digit (64-bit) key to the base encryption.